Note 7 - Marketable Securities - Short-term and Long-term Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost	$ 93,445	$ 48,397
Unrealized Gains	393	112
Unrealized Losses	(23)	(22)
Fair Value	93,815	48,487
Bank Time Deposits [Member]
Amortized Cost	5,395	1,484
Unrealized Gains	93	22
Unrealized Losses	0	0
Fair Value	5,488	1,506
US Government Agencies Debt Securities [Member]
Amortized Cost	18,500	6,274
Unrealized Gains	6	1
Unrealized Losses	(10)	(7)
Fair Value	18,496	6,268
Corporate Debt Securities [Member]
Amortized Cost	42,048	26,944
Unrealized Gains	211	80
Unrealized Losses	(11)	(12)
Fair Value	42,248	27,012
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	25,003	10,204
Unrealized Gains	83	9
Unrealized Losses	(2)	(3)
Fair Value	25,084	10,210
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	2,499	3,491
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 2,499	$ 3,491